Since that date, Apple has received more orders than it had planned for, said Greg Joswiak, vice president of hardware product marketing at Apple. The number of orders--which included more than 100,000 preorders, according to Apple--was high enough to outstrip the availability of the 4GB drive from its manufacturer.

Apple was forced to concentrate on filling orders from the U.S. market and to wait for greater availability of the drive in order to enter the international market, he said.

"We expected it to be a hit, but (demand) is turning out to be stronger than expected," Joswiak said. "U.S. demand is going to consume all the supply we had planned through June."

The 4GB hard drive at the center of the iPod Mini came out in January, around the same time Apple announced the device. Its manufacturer, reported to be Hitachi, is still ramping up, so the supply of the drives has been limited, Joswiak explained.

Right now, "The (iPod Mini) demand is consuming just about all the 4GB 1-inch drives being made," he said.

Once the manufacturer increases the number of drives it produces, Apple will be able to expand the sales of the iPod Mini. Apple plans to begin that process in July. The company has yet to announce which countries the player will be offered in.

The iPod Mini's 4GB capacity allows it to store up to 1,000 songs, Apple has said. It also comes in five colors--silver, gold, pink, blue and green--and works with Apple's iTunes online music store.

Apple also continues to market its original iPod in 15GB, 20GB and 40GB capacities at prices ranging from $299 for the 15GB model to $499 for the 40GB model.

The release of the iPod Mini, as well Apple's partnership with Hewlett-Packard to sell an HP-branded version of the iPod, should help fuel Apple's momentum in the portable music player market. Right now, the company is king of the hill in that market, analysts say.

During February, the iPod player was the top portable music player at retail in the U.S. iPod unit sales--including about two weeks worth of iPod Mini unit sales--captured about 33 percent of unit sales in the category at retail in the United States, according to NPD Techworld. It had 25 percent of that market in January and 20 percent in December, the firm said.

But while its dominance at retail helps iPod's in the wider market for portable music players, "I wouldn't say they own it," said Steve Baker, analyst with NPD. Baker said that the RCA Lyra, and Digital Networks North America's Rio are two of Apple's main competitors at retail.

"There are a lot of products out there that are doing well...and there's a lot of ways you can compete with Apple, including on price," Baker said. Right now, for example, Apple is "not addressing the $99 or $149, more limited use (music player) market," he said.